1. Field of the Invention
The present invention relates generally to digital communication systems and, more particularly, relates the transmission of encrypted data over a time division multiplexing system.
2. Description of the Relevant Art
The increasing prevalence of digital communications systems has led to the widespread use of digital encryption systems by governments and other entities concerned with the security of sensitive data.
Generally, an encryption system includes an encryption device that scrambles the bit locations in a data stream to render the data stream unintelligible. A corresponding decryption device unscrambles the encrypted data stream to return the bit locations to their original locations.
Unfortunately, this encryption technique prevents the use of the increasingly popular and costeffective time division multiplexing (TDM) systems such as T1. In the T1 system 8-bit words from 24 channels sampled at 8 KHz are included as the first 192 bits in a frame. The 193rd bit in each frame is a T1 framing bits so that the frames must be transmitted at 1.544 MHz. These framing bits are utilized at a T1 receiver to define the T1 frames and route the correct 8-bit words to the corresponding channel.
If T1 formatted data were scrambled by an encryption device, then the T1 framing bits would be randomly scattered throughout the scrambled bit stream. Thus, the scrambled data is no longer in the correct T1 format and cannot be transmitted over a T1 system. Accordingly, the transmission of encrypted data has required the use of special dedicated lines thereby decreasing the flexibility and increasing the cost of transmission relative to the cost of using T1.
It is thus apparent that a system for facilitating the use of a standard TDM system for transmitting encrypted data would be of great benefit to the art.